In memory, an image may be defined by a matrix of pixels occupying N lines and P columns. In some cases, the sampled and digitized image is represented by a sequence of 0s and 1s disposed in lines and columns in the matrix and the proposed device then serves to directly locate memory cells that contain a 1 (or a 0).
In general, such digitized images are analyzed by reading the matrix memory sequentially and testing each pixel to determine whether it satisfies a predetermined condition. The term "excited" is used below to designate a pixel which satisfies the condition since, in general, the condition relates to whether the pixel is to be considered as being illuminated or not.
Such sequential reading necessarily leads to scanning the entire memory even if the number of excited pixels is small compared with the total number of pixels in the memory. This gives rise to a waste of time which considerably reduces the speed at which the image can be read.
The object of the invention is to provide a solution to this problem. To this end, the invention provides apparatus capable of processing only useful information, i.e. the excited pixels of a matrix memory.